Sounds like you purchased a handicapped tree. Is it possible to tape a straight piece of wood or metal to the base of the tree with electric tape and bend either branch to a straight vertical position by taping it to this post?

From your description, I think that if you can't bend it straight the big branch will have to go but I'd wait to remove the smaller one even it it can't make a leader by bending it. You should get a strong shoot to become your leader where you cut the big branch. When it is growing well you can gradually reduce the remaining branch and grow new ones off the leader.

Do the initial pruning in very early spring before the tree begins to grow. Most varieties of apples are much more tender when they're young.

Macoun is a difficult variety to train and you will need to spread branches as it is a very upright grower.